The present invention relates to a composition useful for coating and printing for baking finish, particularly a coating composition and printing ink composition for baking finish on an outer surface of a can.
For application to an outer surface, particularly application to an outer surface of a can, a thermosetting organic solvent coating composition or aqueous coating composition or a radiation crosslinking coating composition has been used.
A thermosetting organic solvent coating composition is excellent from the point that since an organic solvent has a high diluting ability, solid components having properties necessary for application on an outer surface of a can are easily blended in the composition, particularly from the point that a coating film excellent in water resistance and retort resistance can be formed. However there is a fear that at the time of application and baking, a great amount of solvent is released into an atmosphere, which results in environmental pollution, i.e., contamination of atmosphere, and besides that, solvent resistance of the obtained film is not enough since a resin thereof has lipophilic property. Also since such a coating composition is a hazardous material, sufficient control against fires is required.
A thermosetting aqueous coating composition is a non-hazardous material. Therefore it is easy to handle from the viewpoint of fire, and is excellent from the point that there is less possibility of causing contamination of atmosphere at the time of application. However much energy and time are required for baking, and since a resin thereof is hydrophilic, water resistance and retort resistance of the obtained coating film are not sufficient.
Those organic solvent coating composition and aqueous coating composition are usually applied on a can by roll coating method. In that case, since a resin content (solid content) in the coating composition is small, in order to obtain a desired coating thickness, it is necessary to apply much amount of coating composition on an outer surface of a can. However as a coating amount increases, a scattering amount of coating composition (called xe2x80x9cmistingxe2x80x9d) also increases, which causes problems that working environment is deteriorated and inner and outer surfaces of the can are stained.
On the other hand, radiation (ultraviolet ray) crosslinking coating composition itself is substantially solid after reaction, and therefore is excellent in that a scattering amount is small at the time of application and there is less possibility of causing contamination of atmosphere. However since a coating film shrinks at the time of curing, adhesion to a can and processability or dimensional stability are not sufficient, and besides that, curing of a coating film is insufficient only by curing with radiation and further baking step is required. Also an expensive curing catalyst which has radiosensitivity is necessary, and thus an increase in cost of coating composition itself is resulted.
For example, in U.S. Pat. No. 4,230,740, a photo curable composition comprising a melamine (meth)acrylate resin having six reactive double bonds is disclosed, and in U.S. Pat. No. 4,230,550, a photo curable coating comprising a melamine acrylate resin having three methoxymetyl groups is disclosed. However since those melamine (meth)acrylate resins have many reaction moieties (crosslinking points), a crosslinking density becomes high, which results in a hard and fragile coating film.
Further a polymerizable melamine (meth)acrylate resin is disclosed in U.S. Pat. No. 3,020,255. However a chain length of an acrylate portion of that melamine (meth)acrylate is short (the number of carbon atoms does not exceed 4), and a change in its properties easily occurs. Also an elongation of an obtained coating film is small and there is a case where cracking of a coating film occurs when processing a coated article.
An object of the present invention is to solve the above-mentioned problems and provide a composition for coating and printing for baking finish which has the following advantages.
(1) Application by roll coating method and printing by using a block material for printing are possible, and a coating amount can be reduced to a minimum, thus making it possible to inhibit an amount of a composition scattering from a roll or block material to a minimum and minimize deterioration of working environment and contamination of printed article, particularly contamination of inner and outer surfaces of a can.
(2) The composition contains neither organic solvent nor water or contains only a small amount thereof, and therefore almost all the components of the composition become substantially solid after thermosetting and no energy or only a small amount of energy is required for evaporating the solvent.
(3) A coating film excellent in solvent resistance, water resistance, abrasion resistance and scratch resistance can be formed.
(4) An expensive curing catalyst is not used or its amount is decreased greatly.
The present invention relates to the composition for coating and printing for baking finish, which contains a specific benzoguanamine compound (A) having a radically polymerizable double bond and condensation-polymerizable functional group in its molecule and a radically polymerizable compound (B) which is a specific modified (meth)acrylate.
The compound (A) comprises one or two or more compounds represented by the formula (I): 
wherein R1 is phenyl; R2 is H, an alkyl group having 5 to 18 carbon atoms, cyclohexyl, phenyl or R3, R4 or R5 described below; n is 0 or an integer of 1 to 3; provided that at least one of R2 in one molecule is R3, R4 or R5, in which R3 is a group represented by the formula (1):
xe2x80x94Xxe2x80x94OCOxe2x80x94CYxe2x95x90CH2xe2x80x83xe2x80x83(1)
in which Y is H or xe2x80x94CH3; X is an alkylene group having 5 to 18 carbon atoms and a part or a whole of its hydrogen atoms may be substituted by halogen atom, R4 is a group represented by the formula (2):
xe2x80x94(Vxe2x80x94O)mxe2x80x94Zxe2x80x94OCOxe2x80x94CYxe2x95x90CH2xe2x80x83xe2x80x83(2)
in which Y is as defined above; each of V and Z is a linear or cyclic alkylene group having 2 to 8 carbon atoms and a part or a whole of its hydrogen atoms may be substituted by halogen atom, m is an integer of 1 to 20, and R5 is a group represented by the formula (3):
xe2x80x94(Wxe2x80x94COO)pxe2x80x94Zxe2x80x94OCOxe2x80x94CYxe2x95x90CH2xe2x80x83xe2x80x83(3)
in which Y and Z are as defined above; W is a linear or cyclic alkylene group having 3 to 8 carbon atoms and a part or a whole of its hydrogen atoms may be substituted by halogen atom, p is an integer of 1 to 8.
The radically polymerizable modified (meth)acrylate compound (B) is
(1) an alkyleneoxide-modified (meth)acrylate prepared by reacting (meth)acrylic acid with an alcohol having ethyleneoxide or propyleneoxide adduct, a carboxyalkylester-modified (meth)acrylate prepared by reacting a carboxyalkyl (meth)acrylate with an alcohol, an epoxy-modified (meth)acrylate prepared by reacting acrylic acid or methacrylic acid with epoxy group of glycidyl ether of an alcohol, a (meth)acrylate having urethane bond and prepared by reacting a (meth)acrylate having hydroxyl with a compound having isocyanate group at its end or a mixture thereof; or
(2) a (meth)acrylate-modified epoxy resin prepared by reacting (meth)acrylic acid with an epoxy resin, a (meth)acrylate-modified epoxy resin prepared by reacting (meth)acrylic acid with the epoxy resin modified by the above-mentioned alkyleneoxide or carboxylalkyl, a (meth)acrylate prepolymer or polymer having urethane bond and prepared by reacting a (meth)acrylate having hydroxyl with a compound having isocyanate group at its end, a (meth)acrylate-modified polyester prepared by reacting (meth)acrylic acid with a polyester, or a mixture thereof.
It is preferable that the compound (A) is the compound represented by the formula (I), in which 1 to 5 of R2 is one or two or more of R3, R4 or R5.
Further it is preferable that the compound (A) is a benzoguanamine acrylate resin, in which in the formula (I), Y in R3, R4 or R5 is H; and a benzoguanamine methacrylate resin, in which in the formula (I), Y in R3, R4 or R5 is CH3.
It is preferable that the composition of the present invention contains an initiator exhibiting a catalytic ability in the condensation polymerization and/or an initiator exhibiting a catalytic ability in the radical polymerization, and that no solvent is contained (solvent-less) or its amount is as small as not more than 20% by weight (composition of high solid content). Also a reactive additive may be contained in the composition.
The composition of the present invention is for baking finish and is used as a coating composition for baking finish when coated and as a printing composition for baking finish when printed. There is no substantial difference between the coating for baking finish and the printing for baking finish except that in the latter case of printing, letters and patterns are formed partly by using a block material for printing. Therefore the following explanation is made with respect to the former coating composition for baking finish unless otherwise noted.